It is well-known to use digital storage facilities and a programmed computer to provide, respectively, a data base storage medium and a data base manager. The storage facilities serve to store large amounts of information in digital form while the data base manager is a computer program facility for accessing, searching and changing the information in the data base.
Such data base systems are often used to provide an inventory of physical facilities available to a community of users. The facilities may, for example, from time to time be assigned for exclusive use by one of the users to the exclusion of others. A system for airline seat reservations, automobile rental reservations or computer center resource allocation are illustrative of the types of data base systems involving the temporary assignment of facilities to users.
When facilities are temporarily assigned to one user and later are reassigned to another user, the assignment and reassignment of those facilities can react to the instantaneous demand of users for facilities, or can be scheduled out into the future by assignment algorithms which optimize the use of the facilities in some way. In the latter case, it is necessary not only to keep track of the current assignments of facilities to users, but also to keep track of future reassignments of those same facilities to different users.
The general problem of representing future versions of a data base as well as the current version is a complicated problem. Complexity is compounded when processing must be done with such future versions as well as with the current version.